PROJECT ABSTRACT With the career goal of becoming an independent health services researcher, Dr. Susan Calcaterra describes a mentored research project and a rigorous career development plan which will prepare her to become a leader in the integration of opioid use disorder (OUD) treatment in the hospital setting with linkage to OUD care post discharge. Nearly 200 people died every day from an overdose in 2017 in the United States (US). In 2012, there were 527,000 hospitalizations due to opioid use which cost more than $15 billion in medical care. For patients with OUD, there are proven benefits to initiating buprenorphine in the hospital with treatment referrals and prescribing naloxone at discharge. Unfortunately, OUDs are often not addressed in the hospital resulting in a missed opportunity to provide patients evidence-based treatment. There are 50,000 hospital-based physicians (hospitalists) caring for hospitalized patients in the US. This vast workforce offers a potential solution to initiate buprenorphine in the hospital, provide naloxone at discharge, and ensure patients are referred to ongoing OUD treatment. There is a critical need to determine why buprenorphine and naloxone are not routinely prescribed to hospitalized patients with OUD and to sustainably integrate evidence-based OUD treatment in the hospital using the existing workforce. Without this knowledge, many hospitalized patients will fail to receive lifesaving medication. The proposed research centers on the hypothesis that hospitalist?s knowledge and beliefs impact OUD treatment and the hospital?s current structures and processes do not support OUD treatment. Study Aims include: 1) a qualitative investigation into key barriers to the integration of evidence-based OUD care into hospital practice in three academic hospitals with hospitalists, psychiatrists, pharmacists, social workers and nurses; 2) the development of a multicomponent intervention that adapts evidence-based OUD treatment to the hospital setting by addressing reported barriers in Aim 1 and by systematically meeting the needs of hospitalists, nurses, pharmacists and social workers within their workflow; and 3) pilot test a multicomponent intervention to improve OUD treatment in one hospital over 12 months. Use the RE-AIM framework to measure changes in buprenorphine and naloxone prescribing (Reach) and changes in the number of providers licensed to prescribe buprenorphine (Adoption) pre/post intervention implementation. Interview hospital providers to identify ongoing Implementation barriers and to learn about adaptations made to the intervention to improve its efficiency and ease of use. To accomplish these aims, Dr. Calcaterra will pursue training in 1) qualitative research methods to inform the intervention development, 2) intervention development to modify healthcare provider behaviors, and 3) dissemination and implementation science for future intervention dissemination. Upon completion of these activities, along with intensive mentorship, Dr. Calcaterra will be positioned to conduct a larger comparative effectiveness trial to further implement, test and refine the intervention?s fidelity (future R01).